Content distribution system, network, and channel switching control method

ABSTRACT

A content distribution system uses a PtP (point to point) channel (individual channel) or PtM (point to multi-point) channel (common channel) as a radio channel of a predetermined type so as to distribute a broadcast content as communication data to a user terminal as a mobile station. The user terminal receives the same content distributed from a broadcast content server by the PtP channel. Here, if the total of the downlink transmission power of the PtP channel is greater than the downlink transmission power of the PtM channel when the content is distributed to the user terminal by the single PtM channel, a base station or a base station control device judges that the radio channel is to be switched from the PtP channel to the PtM channel. Similar judgment is made when switching from the PtM channel to the PtP channel is performed. Thus, it is possible to switch the radio channel type used for the broadcast-type service without lowering the use effect of the radio resources.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No.2003-3810 filed on Jan. 10, 2003, the contents of which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a content distribution system, anetwork, and a channel switching control method, and more particularly,to a content distribution system that switches the type of radiochannels used for a content distribution.

BACKGROUND ART

A broadcast-type service includes both a broadcast and multicastservices, and provides the same content for a plurality of userterminals existing within the cell of each base station at the sametime. The user terminal receiving the broadcast-type service within thecell should be able to receive content with a certain quality of service(QoS) as far as it is located within the area. To that end, a sufficientreceiving power needs to be provided for the respective user terminals.

The broadcast-type service is realized by a point to multi-point (PtM)system or a point to point (PtP) system.

In the PtM system, a base station uses a single point to multi-pointchannel (common channel) reaching the cell boundary to distributecontent to all user terminals within the cell. The PtM system is alsoreferred to as “common channel system”.

In the PtM system, a single downlink radio channel is used to distributecontent to the user terminals, so that even in the case where a largenumber of the user terminals in the broadcast-type service area receivethe content at the same time, the base station need not increase atransmission power of the radio channel irrespective of the number ofthe user terminals.

Therefore, with the PtM system, it is possible to increase the useeffect of the radio resources in the case where a large number of theuser terminals receive the broadcast-type service within the cell. Whenthere is a sufficient downlink power capacity available in the operationof the broadcast-type service, it is possible for the base station todistribute content to all the user terminals within the cell byperforming control such that the downlink transmission power of the PtMchannel can reach the cell boundary. On the other hand, when there isnot a sufficient downlink power capacity available, the base stationperforms control to set the downlink transmission power of the PtMchannel to a value less than the downlink transmission power with whichthe PtM channel can reach the cell boundary. In this case, therefore,the base station can distribute content only to a part of the userterminals in the cell. That is, the user terminals near the cellboundary cannot receive the PtM channel and thereby cannot receivecontent.

In the PtP system, a base station uses point to point channels(individual channels) for respective user terminals to distribute thesame content to the user terminals subscribing to the broadcast-typeservice within the cell. The PtP system is also referred to as“individual channel system”.

The PtP system is used when there are a comparatively small number ofuser terminals subscribing to the broadcast-type service within thecell. The PtP system uses the individual channel, so that the basestation can set the downlink transmission power of the individualchannel to an adequate value by performing transmission power control.Therefore, when the number of the user terminals is comparatively small,it is possible to reduce the downlink transmission power fordistributing content to the user terminals.

As described above, the PtP and PtM systems are available for realizingthe broadcast-type service. Here, in order to determine to use which ofthe PtP and PtM systems, it is necessary to make a determination basedon the radio environmental capacity of the radio communication resourcesestimating the respective downlink transmission power.

Disclosed in a non-patent document (3GPP TR 23.846 1.2.0, September,2002, P.17) is that the radio channel type (point to multi-point orpoint to point) is determined based on the number of the user terminalssubscribing to the broadcast-type service within the cell.

In the case where the radio channel type is determined based on thenumber of the user terminals subscribing to the broadcast-type servicewithin the cell as described above, it is considered that the PtPchannel is used when the number of the user terminals is not more than acertain threshold value and the PtM channel is used when the numberthereof exceeds the threshold value.

However, the above method of determining the radio channel type used forthe content distribution based on the number of the user terminalssubscribing to the broadcast-type service within the cell has thefollowing problem.

For example, in the case where the single PtM channel is used todistribute content to the user terminals subscribing to thebroadcast-type service within the cell, when the number of the userterminals changes to become not more than a certain threshold value, theradio channel used for the content distribution is switched from the PtMchannel to PtP channel, and the PtP channel is used to distribute thecontent to the respective user terminals. However, if all the userterminals are located near the cell boundary, the total of thetransmission power of the PtP channel for the user terminals becomesgreater than the transmission power of the PtM channel.

That is, in some cases, the switching function of the radio channel usedfor the content distribution based on the number of the user terminalslowers, rather than increases, the use effect of the radio resources.Therefore, it is necessary to perform the switching based on theabovementioned radio environmental capacity of the radio communicationresources.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a content distributionsystem, a network, and a channel switching control method capable ofswitching the type of radio channels used for a broadcast-type serviceby a determination based on the radio environmental capacity of theradio communication resources without lowering the use effect of theradio resources.

A content distribution system according to the present invention ischaracterized by comprising a channel switching determination means fordetermining whether the type of the communication channel sent from abase station to mobile station is switched based on the power forcontent distribution from the base station to the mobile station.

A channel switching control method according to the present invention isa channel switching control method of a content distribution system thatdistributes the content to a mobile station and is characterized bycomprising a channel switching determination step of determining whetherthe type of the communication channel sent from a base station to themobile station is switched based on the power for content distributionfrom the base station to the mobile station.

A network according to the present invention is characterized bycomprising a channel switching determination means for determiningwhether the type of the communication channel sent from the base stationto the mobile station is switched based on the power for contentdistribution from the base station to mobile station.

A channel switching control method according to the present invention isa channel switching control method of a network that distributes thecontent to a mobile station and is characterized by comprisingdetermining whether the type of the communication channel sent from thebase station to the mobile station is switched based on the power forcontent distribution from the base station to mobile station.

According to the present invention, it is determined whether the type ofa communication channel sent from the base station to mobile station isswitched based on the power for content distribution from the basestation to mobile station. This switching of the communication channeltype used for the content distribution prevents the use effect of theradio resources from lowering.

The effect of the present invention is to switch the radio channel typeused for the broadcast-type service without lowering the use effect ofthe radio resources. This is because it is determined whether the radiochannel type sent from the base station to mobile station is switchedbased on the power for content distribution from the base station tomobile station. The present invention allows a selection of a radiochannel type appropriate for the situation of the radio resources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a configuration of a mobile communicationsystem according to an embodiment of the present invention;

FIG. 2 is a flowchart showing an operation of the mobile communicationsystem according to the embodiment of the present invention in the casewhere a PtP channel is used to provide a broadcast-type service;

FIG. 3 is a flowchart showing an operation subsequent to the operationshown in FIG. 2;

FIG. 4 is a flowchart showing an operation of the mobile communicationsystem according to the embodiment of the present invention in the casewhere a PtM channel is used to provide a broadcast-type service;

FIG. 5 is a flowchart showing an operation subsequent to the operationshown in FIG. 4;

FIG. 6 is a view for explaining a state between a base station and userterminals located within the cell of the base station in the case wherea channel switching process is performed in the operation of the mobilecommunication system according to the embodiment of the presentinvention;

FIG. 7 is a view for explaining a state between a base station and userterminals located within the cell of the base station in the case wherea channel switching process is performed in the operation of the mobilecommunication system according to the embodiment of the presentinvention;

FIG. 8 is a view for explaining a state between a base station and userterminals located within the cell of the base station in the case wherea channel switching process is performed in the operation of the mobilecommunication system according to the embodiment of the presentinvention;

FIG. 9 is a view for explaining a state between a base station and userterminals located within the cell of the base station in the case wherea channel switching process is performed in the operation of the mobilecommunication system according to the embodiment of the presentinvention;

FIG. 10 is a view for explaining a state between a base station and userterminals located within the cell of the base station in the case wherea channel switching process is performed in the operation of the mobilecommunication system according to the embodiment of the presentinvention;

FIG. 11 is a view for explaining a state between a base station and userterminals located within the cell of the base station in the case wherea channel switching process is performed in the operation of the mobilecommunication system according to the embodiment of the presentinvention;

FIG. 12 is a view for explaining a state between a base station and userterminals located within the cell of the base station in the case wherea channel switching process is performed in the operation of the mobilecommunication system according to the embodiment of the presentinvention;

FIG. 13 is a view for explaining a state between a base station and userterminals located within the cell of the base station in the case wherea channel switching process is performed in the operation of the mobilecommunication system according to the embodiment of the presentinvention;

FIG. 14 is a view for explaining a state between a base station and userterminals located within the cell of the base station in the case wherea channel switching process is performed in the operation of the mobilecommunication system according to the embodiment of the presentinvention;

FIG. 15 is a view for explaining a state between a base station and userterminals located within the cell of the base station in the case wherea channel switching process is performed in the operation of the mobilecommunication system according to the embodiment of the presentinvention;

FIG. 16 is a view for explaining a state between a base station and userterminals located within the cell of the base station in the case wherea channel switching process is performed in the operation of the mobilecommunication system according to the embodiment of the presentinvention;

FIG. 17 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step S7)shown in FIG. 3 is performed under the condition shown in FIG. 6;

FIG. 18 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step S7)shown in FIG. 3 is performed under the condition shown in FIG. 8;

FIG. 19 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step S7)shown in FIG. 3 is performed under the condition shown in FIG. 10;

FIG. 20 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step S9)shown in FIG. 3 is performed under the condition shown in FIG. 6;

FIG. 21 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step S9)shown in FIG. 3 is performed under the condition shown in FIG. 8;

FIG. 22 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step S9)shown in FIG. 3 is performed under the condition shown in FIG. 10;

FIG. 23 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step S7)shown in FIG. 3 is performed under the condition shown in FIG. 6;

FIG. 24 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step S10)shown in FIG. 3 is performed under the condition shown in FIG. 16;

FIG. 25 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step T7)shown in FIG. 5 is performed under the condition shown in FIG. 12;

FIG. 26 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step T7)shown in FIG. 5 is performed under the condition shown in FIG. 10;

FIG. 27 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step T7)shown in FIG. 5 is performed under the condition shown in FIG. 8;

FIG. 28 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step T10)shown in FIG. 5 is performed under the condition shown in FIG. 12;

FIG. 29 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step T10)shown in FIG. 5 is performed under the condition shown in FIG. 10;

FIG. 30 is a sequence chart showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the channel switching process (step T10)shown in FIG. 5 is performed under the condition shown in FIG. 8; and

FIGS. 31A and 31B are sequence charts each showing an operation of themobile communication system according to the embodiment of the presentinvention in the case where a content attribute notification process andcontent attribute changeover process between a base station controldevice and broadcast content server.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described below withreference to the accompanying drawings. In the following description,the same reference numerals denote the same parts through the drawings.

FIG. 1 is a view showing a configuration of a mobile communicationsystem (content distribution system) according to the embodiment of thepresent invention. The mobile communication system according to theembodiment is applied to a mobile phone, a PHS (Personal HandyphoneSystem) and the like.

As shown in FIG. 1, the mobile communication system according to thepresent embodiment includes user terminals 101 to 103 corresponding tomobile stations (MS), base station devices (BS) 201 and 202, a basestation control device (RNC: Radio Network Controller) 301, a networkconnection device 401, and a broadcast content server 501.

The user terminals 101 to 103 are terminals that the users enjoying amobile communication service provided by the mobile communication systemaccording to the present embodiment have and carry. The user terminals101 to 103 can receive the mobile communication service within the areathat the mobile communication system covers.

A mobile phone or PHS (Personal Handyphone System) terminal can be takenas an example of the user terminals 101 to 103. In the presentembodiment, any access method including a CDMA (Code Division MultipleAccess), TDMA (Time Division Multiple Access), and the like can be usedand any digital modulation method including a PSK (Phase Shift Keying),QPSK (Quadrature PSK), p/4 shift QPSK, OQPSK (Offset QPSK), HPSK (HybridPSK) can be used.

Although the internal configuration of each of the user terminals 101 to103 differs depending on the employed access method and digitalmodulation method, it is possible to employ a configuration well knownto those skilled in the art in any case. Therefore, although not shownin the drawing, each of the user terminals 101 to 103 functionallyincludes a radio section (a transmission circuit having an antenna,duplexer, modulator, and power amplifier and a reception circuit havinga demodulator), a control section (a system controller and the like)which controls the entire operation, and a signal processing section(voice codec for voice coding/decoding, channel codec forcoding/decoding control information (message) required for communicationbetween the base station and mobile station) and executes a processingoperation along respective process flows shown in sequence charts (to bedescribed later) of the accompanying drawings under the control of thecontrol section. The processing operation is realized when, for example,a CPU in the control section executes a control program stored in areadable manner on a memory.

When being located within the cell of the base station device 201, theuser terminals 101 to 103 can communicate with the base station device201 through a radio medium; similarly, when being located within thecell of the base station device 202, the user terminals 101 to 103 cancommunicate with the base station device 202 through a radio medium.

The base station devices 201 and 202 are provided within the area thatthe mobile communication system covers. The base station devices 201 and202 are connected to the network connection device 401 through the basestation control device 301.

The base station device 201 and 202 may be mounted on, for example, amobile phone base station or PHS base station. In the presentembodiment, any access method including a CDMA, TDMA, and the like canbe used and any digital modulation method including a PSK, QPSK, p/4shift QPSK, OQPSK, HPSK and the like can be used.

Although the internal configuration of each of the base station devices201 and 202 differs depending on the employed access method and digitalmodulation method, it is possible to employ a configuration well knownto those skilled in the art in any case. Therefore, although not shownin the drawing, each of the base station devices 201 and 202functionally includes a radio section (a transmission circuit having anantenna, duplexer, modulator, and power amplifier and a receptioncircuit having a demodulator), a control section (a system controllerand the like) which controls the entire operation, and a signalprocessing section (voice codec for voice coding/decoding, channel codecfor coding/decoding control information (message) required forcommunication between the base station device and user terminal (mobilestation)) and executes a processing operation along respective processflows shown in sequence charts (to be described later) of theaccompanying drawings under the control of the control section. Theprocessing operation is realized when, for example, a CPU in the controlsection executes a control program stored in a readable manner on amemory.

The base station control device 301 has functions of relaying areception signal and assigning a radio channel (communication channel)for transmitting a radio signal between respective user terminals andbase station devices. The respective functions are realized when, forexample, a CPU in an incorporated controller executes a control programstored on a memory and thereby executes a processing operation alongrespective process flows shown in sequence charts (to be describedlater) of the accompanying drawings.

The base station devices 201, 202 and base station control device 301constitute a RAN (Radio Access Network). The content distributionsystem, network channel switching control means, and channel switchingcontrol method according to the present invention function in theprocessing operations realized by the program control of the basestation devices 201, 202, and/or base station control device 301 in thisembodiment.

The network connection device 401 is connected to, for example, a publictelephone network, public data network, private network, facility of thevarious service providers (not shown) and is also connected to thebroadcast content server 501.

The broadcast content server 501 is, for example, constituted by one ormore computer machines such as a PC (Personal Computer) or a dedicatedserver connected to a network in a communicable manner and operatesunder the program control of a CPU in the machine. The broadcast contentserver 501 stores various contents for the broadcast-type service, whichis one of mobile communication services, in the data storage areaassigned on a storage medium such as a memory or hard disk as data to beprocessed (table or database) by the CPU. The content of the broadcastcontent server 501 is distributed to users subscribing to variousservice providers. The content is distributed to the user terminals 101to 103 through the network connection device 401, base station controldevice 301, and base station device 201 or 202.

As a radio channel type for distributing the same content to the userterminals 101 to 103 to be provided with the broadcast-type service atthe same time, a point to multi-point (PtM) and point to point (PtP) areavailable.

According to the embodiment of the present invention, when the userterminals 101 to 103 receive the content on the PtP channel (individualchannel), it is determined whether the radio channel for the contentdistribution is switched from the PtP channel to the single PtM channelbased on the total of the downlink transmission power of the PtP channeland the downlink transmission power of the single PtM channel (commonchannel) used for distributing the content to the user terminals 101 to103.

When the user terminals 101 to 103 receive the content on the single PtMchannel, it is determined whether the radio channel for the contentdistribution is switched from the PtM channel to the PtP channel basedon the downlink transmission power of the PtM channel and the total ofthe downlink transmission power of the PtP channel used for distributingthe content to the user terminals 101 to 103.

When the radio channel type is switched, a switching process isperformed in such a manner not to interrupt the content receptionoperation of the user terminals 101 to 103, or with an interruption.

In the case where the switching process is performed without theinterruption of content reception, while one radio channel currentlyused for the content distribution to the user terminals 101 to 103 ismaintained, the other radio channel is set. Further, the switchingprocess is performed such that the total of the power of thetransmission from the base station that transmits the content to theuser terminals 101 to 103 to all the user terminals (user terminals 101to 103 and not-shown user terminals that do not subscribe to thebroadcast-type service) within the cell of the base station does notexceed the upper limit of the transmission power that the base stationcan output to the cell during the time period when these radio channelsdifferent from each other are concurrently set.

In the case where the switching process is performed with theinterruption of content reception, one radio channel currently used forthe content distribution to the user terminals 101 to 103 is canceled,and the other radio channel is then set. Also in this case, theswitching process is performed such that the total of the downlinktransmission power of the base station does not exceed the upper limitduring the switching process time.

Hereinafter, an operation of the mobile communication system accordingto the embodiment of the present invention in the case where theplurality of user terminals subscribing to the broadcast-type servicewithin the cell of the base station 201 receive the content on the PtPchannel will be described with reference to the drawings.

FIGS. 2 and 3 are flowcharts each showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the PtP channel is used to provide thebroadcast-type service.

The processing procedure shown in FIGS. 2 and 3 is activated when anyuser terminal within the cell of the base station 201 requests thebroadcast-type service or when the user terminal that has alreadyrequested the broadcast-type service enters the cell. That is, theprocessing procedure is activated every time the number of the userterminals within the cell that receives the broadcast-type service onthe PtP channel increases.

Alternatively, the processing procedure shown in FIGS. 2 and 3 may beperiodically activated with a predetermined interval. The reason for theabove is that even when the number of the user terminals that receivethe broadcast-type service on the PtP channel is not changed, thesituation in which the PtP channel needs to be switched to the PtMchannel depending on the location of the user terminal can occur. Forexample, in the case where the user terminal to receive thebroadcast-type service on the PtP channel moves to increase the downlinktransmission power of the PtP channel (in general, in the case where theuser terminal moves away from the base station antenna), the abovesituation can occur.

Alternatively, the processing procedure shown in FIGS. 2 and 3 may beactivated when the allowable number of users that receive thebroadcast-type service is reduced. A mobile communication service of themobile communication system is classified into the broadcast-typeservice that provides the same content to a plurality of users and anon-broadcast-type service that individually provides a telephoneservice, E-mail service, or the like to the respective users. The timingthat causes the allowable number of users that receive thebroadcast-type service or non-broadcast-type service to be increased orreduced is determined depending on the allocation of the service to beprovided to the users located in respective radio areas. When theallowable number of users that receive the broadcast-type service isreduced, the transmission power that can be used for distribution of thebroadcast-type service is restricted to a lower value, with the resultthat the number of the user terminals that can receive thebroadcast-type service on the PtP channel is reduced. Accordingly, theprocessing procedure shown in FIGS. 2 and 3 is activated to determinewhether a switching process from the PtP channel to the PtM channel isperformed. In this case, there is a possibility that a part of the userterminals, which require more power, cannot receive the content.

Alternatively, the processing procedure shown in FIGS. 2 and 3 may beactivated when the allowable number of users that receive thenon-broadcast-type service is increased. When the allowable number ofusers that receive the non-broadcast-type service is increased, thetransmission power that can be used for distribution of thebroadcast-type service is restricted to a lower value, with the resultthat the number of the user terminals that can receive thebroadcast-type service on the PtP channel is reduced. Accordingly, theprocessing procedure shown in FIGS. 2 and 3 is activated to determinewhether a switching process from the PtP channel to the PtM channel isperformed. Also in this case, there is a possibility that a part of theuser terminals, which require more power, cannot receive the content.Alternatively, the processing procedure shown in FIGS. 2 and 3 may beactivated when the total of the transmission power of the PtP channelused for the content distribution exceeds a predetermined value.

When one of the abovementioned conditions is satisfied to activate theprocessing procedure shown in FIGS. 2 and 3, the base station controldevice 301 orders the base station 201 to recognize the transmissionpower of all the PtP channels that the user terminals to receive thebroadcast-type service in the cell of the base station 201 are using.The base station 201 then recognizes the transmission power of all thePtP channels, and the base station 201 or base station control device301 calculates the total (TTL_PtP) of the transmission power of all thePtP channels (step S1). The report of the transmission power recognizedby the base station 201 to the base station control device 301 allowsthe base station control device 301 to calculate the total (TTL_PtP).

The base station 201 or base station control device 301 estimates thetransmission power of the PtM channel required to distribute the contentto the user terminal (hereinafter, referred to as “first user terminal”)that is to receive the content on the PtP channel (hereinafter, referredto as “first PtP channel”) having the maximum power of the transmissionpowers of all the PtP channels. That is, the base station 201 or basestation control device 301 estimates the transmission power (Max_PtM) ofthe PtM channel that reaches the first user terminal (step S2). Thetransmission power (Max_PtM) of the PtM channel can be estimated basedon the transmission power of the first PtP channel and measurementinformation from the first user terminal. The measurement informationfrom the first user terminal is information related to reception powerof the first PtP channel. In the estimation process in step S2, thefirst user terminal measures the reception power of the first PtPchannel and reports the measurement result to the base station 201 orbase station control device 301.

The base station 201 or base station control device 301 compares thetotal (TTL_PtP) of the transmission power of the PtP channel andtransmission power (Max_PtM) of the PtM channel that reaches the firstuser terminal (step S3). When the total (TTL_PtP) is less than thetransmission power (Max_PtM) (No in step S3), the base station 201 orbase station control device 301 determines that a switching process fromthe PtP channel to PtM channel need not be performed to end this flowand waits for a new start condition.

On the other hand, when the total (TTL_PtP) is not less than thetransmission power (Max_PtM) (Yes in step S3), the base station 201 orbase station control device 301 determines to perform the switchingprocess from PtP channel to PtM channel and estimates the power margin(Mgn_PW) in the cell of the base station 201 (step S4). The power margin(Mgn_PW) is a difference between the upper limit of the transmissionpower that the base station 201 can output to the cell and the total ofthe transmission power that the base station 201 outputs to all the userterminals (user terminals that receive the broadcast-type service in thecell and user terminals that receive the non-broadcast-type service inthe cell) in the cell.

The base station 201 or base station control device 301 estimates thetransmission power of the PtM channel required to distribute the contentto the user terminal (hereinafter, referred to as “second userterminal”) that is to receive the content on the PtP channel(hereinafter, referred to as “second PtP channel”) having the minimumpower (Min_PtP) of the transmission powers of all the PtP channels. Thatis, the base station 201 or base station control device 301 estimatesthe transmission power (Min_PtM) of the PtM channel that reaches thesecond user terminal (step S5). The transmission power (Min_PtM) can beestimated based on the transmission power of the second PtP channel andmeasurement information from the second user terminal. The measurementinformation from the second user terminal is information related toreception power of the second PtP channel. In the estimation process instep S5, the second user terminal measures the reception power of thesecond PtP channel and reports the measurement result to the basestation 201 or base station control device 301.

In some cases, the transmission power of the PtP channel calculated instep S1 may differ from the initial value at this stage due to movementof the user terminals or the like, the transmission power of all the PtPchannels may be recalculated in step S5.

The base station 201 or base station control device 301 compares thepower margin (Mgn_PW) and the transmission power (Min_PtM) of the PtMchannel that reaches the second user terminal (step S6). When the powermargin (Mgn_PW) is not less than the transmission power (Min_PtM) of thePtM channel that reaches the second user terminal (Yes in step S6), aswitching process from the second PtP channel to PtM channel isperformed (step S7) in such a manner not to interrupt the contentreception operation in the second user terminal. In the channelswitching process, after the PtM channel that reaches the second userterminal is established while the second PtP channel is maintained, thechannel for distributing the content to the second user terminal isswitched from the second PtP channel to the established PtM channel.

On the other hand, when the power margin (Mgn_PW) is less than thetransmission power (Min_PtM) of the PtM channel that reaches the seconduser terminal (No in step S6), the base station 201 or base stationcontrol device 301 compares the value obtained by adding thetransmission power (Min_PtP) of the second Ptp channel to the powermargin (Mgn_PW) and the transmission power (Min_PtM) of the PtM channelthat reaches the second user terminal (step S8).

When “Mgn_PW+Min_PtP≧Min_PtM” is satisfied (Yes in step S8), a channelswitching process for the second user terminal is performed withinterruption of content reception operation (step S9). In this switchingprocess, the PtM channel that reaches the second user terminal isestablished after the second PtP channel has been canceled, and thesecond user terminal receives the content on the established PtMchannel. Therefore, the content reception operation is interrupted inthe second user terminal during the time period between the cancel ofthe second PtP channel and establishment of the PtM channel that reachesthe second user terminal.

When “Mgn_PW+Min_PtP<Min_PtM” is satisfied (No in step S8), a channelswitching process for a plurality of user terminals that receive thebroadcast-type service in the cell of the base station 201 is performedwith interruption of content reception operation (step S10). In thischannel switching process, the PtM channel that reaches all theplurality of user terminals is established after the PtP channel usedfor the content distribution to the plurality of user terminals has beencanceled, and the plurality of user terminals receive the content on theestablished PtM channel. It goes without saying that this channelswitching process is performed such that the total of the downlinktransmission power of the base station 201 does not exceed the upperlimit of the transmission power that the base station 201 can output tothe cell 100.

When the channel switching process (step S10) is performed for all theuser terminals that receive the broadcast-type service in the cell, thetotal of the downlink transmission power of the base station 201 doesnot exceed the upper limit during the channel switching process (stepS10). The reason is that the transmission power (Max_PtM) of the PtMchannel that reaches the first user terminal is not more than the total(TTL_PtP) of the transmission power of the PtP channel (see step S3).

After the process in steps S7, S9, or S10 has been completed, the flowadvances to step S1. The base station 201 or base station control device301, which previously holds a target list in which all the userterminals that receive the broadcast-type service in the cell of thebase station 201 are registered, deletes the user terminals whosereception channel has been switched from the PtP channel to PtM channelin the any of the above steps from the target list (step S1). The basestation 201 or base station control device 301 then determines whetherthe user terminal whose reception channel needs to be switched from PtPchannel to PtM channel exists or not based on the target list (stepS12).

If the user terminal that receives the broadcast-type service on the PtPchannel still exists (Yes in step S12), the base station 201 or basestation control device 301 shifts to step S4. On the other hand, all theuser terminals that receive the broadcast-type service are receiving thecontent on the PtM channel (No in step S12), the base station 201 orbase station control device 301 ends this flow and waits for a new startcondition.

Only a part of the user terminals that receive the broadcast-typeservice in the cell may be registered in the above target list, not allthe user terminals that receive the broadcast-type service in the cell.In this case, a mixed state of the PtP channel and PtM channel may arisetemporary or constantly.

When the power margin (Mgn_PW) is less than the transmission power(Min_PtM) in step S6, it is determined, in step S8, which of the channelswitching processes of steps S9 and step S10 is performed. However, theprocesses in step 8 and step 9 may be omitted. In this case, when thepower margin (Mgn_PW) is less than the transmission power (Min_PtM) instep S6, the channel switching process (step S10) is performed.

When the total (TTL_PtP) is not less than the transmission power(Max_PtM) in step S3 (Yes in step S3), it is determined to perform thechannel switching process from the PtP channel to PtM channel. However,even when the total (TTL_PtP) is not less than the transmission power(Max_PtM), it may be determined not to perform the channel switchingprocess depending on the security attribute of the content. For example,in the case where the content is paid content, the channel switchingprocess may not be performed.

Next, the details of the channel switching process of step S7 (FIG. 3)will be described with reference to the drawings.

FIG. 6 shows a state where the user terminals 101 to 103 located withinthe cell 100 of the base station 201 receive the content on the PtPchannels 1 to 3, and the corresponding parts as those in FIG. 1 areindicated by the same reference numerals. In FIG. 6, the base station201 uses the PtP channel 1 to transmit the content to the user terminal101, uses the PtP channel 2 to transmit the content to the user terminal102, and uses the PtP channel 3 to transmit the content to the userterminal 103. Among the transmission powers of the PtP channels 1 to 3from the base station 201 to user terminals 101 to 103, the transmissionpower of the PtP channel 1 is highest, and that of the PtP channel 3 islowest.

FIG. 17 is a sequence chart showing an operation in the case where thechannel switching process of step S7 (FIG. 3) is performed under thecondition shown in FIG. 6. When the channel switching process of step S7(FIG. 3) is performed under the condition shown in FIG. 6, the basestation control device 301 sends a PtM channel transmission startmessage to the base station 201 to allow the base station 201 to startthe transmission of PtM channel 13 (see FIG. 7) that reaches the userterminal 103, as shown in FIG. 17 (step A1). Upon receiving the PtMchannel transmission start message, the base station 201 starts thetransmission of the PtM channel 13 while maintaining the PtP channel 3as shown in FIG. 7 and returns a transmission start completion messageto the base station control device 301 (step A2).

Upon receiving the transmission start completion message, the basestation control device 301 sends, to the user terminal 103, a switchinginstruction message for instructing the user terminal 103 to receive thecontent not on the PtP channel 3 but on the PtM channel 13 (step A3).Upon receiving the switching instruction message, the user terminal 103starts an operation of receiving the content on the PtM channel 13 andreturns a switching completion message to the base station controldevice 301 after confirming that the content can be received on the PtMchannel 13 in a good condition (step A4).

Upon receiving the switching completion message, the base stationcontrol device 301 sends a PtP channel transmission stop message forcanceling the PtP channel 3 to the base station 201 (step A5). Uponreceiving the transmission stop message, the base station 201 stops thetransmission of the PtP channel 3. As a result, the radio channel usedfor the content distribution to the user terminal 103 is switched fromthe PtP channel 3 to PtM channel 13, and the user terminal 103 receivesthe content on the PtM channel 13, as shown in FIG. 8.

The base station 201 or base station control device 301 may send aninquiry message for inquiring of the user terminal 103 whether or notthe stop of the content reception on the PtP channel 3 and the start ofthe content reception on the PtM channel 13 are possible before thetransmission of the switching instruction message in step A3. In thiscase, the base station 201 or base station control device 301 may sendthe switching instruction message at the time point when receiving an OKreply from the user terminal 103.

However, when receiving a reply indicating that it is impossible toperform a normal content reception from the user terminal 103 as aresult of the inquiry message, the base station 201 or base stationcontrol device 301 rearranges the transmission power of the PtM channel13 based on the current transmission power of the PtP channel 3, thecurrent reception power of the PtP channel 3 measured by the userterminal 103, and the like. After the rearrangement of the transmissionpower of the PtM channel 3, the base station 201 or base station controldevice 301 sends an inquiry message to the user terminal 103 again.

As described above, in FIG. 8, the user terminal 101 receives thecontent on the PtP channel 1, the user terminal 102 receives the contenton the PtP channel 12, and the user terminal 103 receives the content onthe PtM channel 13.

FIG. 18 is a sequence chart showing an operation in the case where thechannel switching process of step S7 (FIG. 3) is performed under thecondition shown in FIG. 8. When the channel switching process of step S7(FIG. 3) is performed under the condition shown in FIG. 8, the basestation control device 301 sends a PtM channel transmission powerincrease message to the base station 201, as shown in FIG. 18 (step A6).The PtM channel transmission power increase message is a message forincreasing the transmission power of PtM channel 13 so as to allow thePtM channel 13 to reach the user terminal 102. Upon receiving thetransmission power increase message, the base station 201 increases thetransmission power of the PtM channel 13. As a result, the PtM channel12 that reaches the user terminal 102 is generated as shown in FIG. 9.Since the transmission power of the PtM channel 12 that reaches the userterminal 102 has been already estimated in step S5 of FIG. 2, the basestation 201 can generate the PtM channel 12 by increasing thetransmission power of the PtM channel 13 based on the estimatedtransmission power of the PtM channel 12.

After generating the PtM channel 12, the base station 201 returns atransmission power increase completion message to the base stationcontrol device 301 (step A7). In response to the transmission powerincrease completion message, the base station control device 301 sends,to the user terminal 102, a switching instruction massage forinstructing the user terminal 102 to receive the content not on the PtPchannel 2, but on the PtM channel 12 (step A8). Upon receiving theswitching instruction message, the user terminal 102 starts an operationof receiving the content on the PtM channel 12 and returns a switchingcompletion message to the base station control device 301 afterconfirming that the content can normally be received on the PtM channel12 (step A9).

Upon receiving the switching completion message, the base stationcontrol device 301 sends a PtP channel transmission stop message forcanceling the PtP channel 2 to the base station 201 (step A10). Uponreceiving the transmission stop message, the base station 201 stops thetransmission of the PtP channel 2. As a result, the radio channel usedfor the content distribution to the user terminal 102 is switched fromthe PtP channel 2 to PtM channel 12, and the user terminals 102 and 103receive the content on the PtM channel 12, as shown in FIG. 10.

The base station 201 or base station control device 301 may send aninquiry message for inquiring of the user terminal 102 whether or notthe stop of the content reception on the PtP channel 2 and the start ofthe content reception on the PtM channel 12 are possible before thetransmission of the switching instruction message in step A8. In thiscase, the base station 201 or base station control device 301 sends theswitching instruction message at the time point when receiving an OKreply from the user terminal 102.

However, when receiving a reply indicating that it is impossible toperform a normal content reception from the user terminal 102 as aresult of the inquiry message, the base station 201 or base stationcontrol device 301 rearranges the transmission power of the PtM channel12 based on the current transmission power of the PtP channel 2, thecurrent reception power of the PtP channel 2 measured by the userterminal 102, and the like. After the rearrangement of the PtM channel12, the base station 201 or base station control device 301 sends aninquiry message to the user terminal 102 again.

As described above, in FIG. 10, only the user terminal 101 receives thecontent on the PtP channel 1, and the user terminals 102 and 103 receivethe content on the PtM channel 12.

FIG. 19 is a sequence chart showing an operation in the case where thechannel switching process of step S7 (FIG. 3) is performed under thecondition shown in FIG. 10. When the channel switching process of stepS7 (FIG. 3) is performed under the condition shown in FIG. 10, the basestation control device 301 sends a PtM channel transmission powerincrease message to the base station 201, as shown in FIG. 19 (stepA11). The PtM channel transmission power increase message in this caseis a message for increasing the transmission power of PtM channel 12 soas to allow the PtM channel 12 to reach the user terminal 101. Uponreceiving the transmission power increase message, the base station 201increases the transmission power of the PtM channel 12. As a result, thePtM channel 11 that reaches the user terminal 101 is generated as shownin FIG. 11. Since the transmission power of the PtM channel 11 thatreaches the user terminal 101 has been already estimated in step S5 ofFIG. 2, the base station 201 can generate the PtM channel 11 byincreasing the transmission power of the PtM channel 12 based on theestimated transmission power of the PtM channel 11.

After generating the PtM channel 11, the base station 201 returns atransmission power increase completion message to the base stationcontrol device 301 (step A12). In response to the transmission powerincrease completion message, the base station control device 301 sends,to the user terminal 102, a switching instruction massage forinstructing the user terminal 101 to receive the content not on the PtPchannel 1, but on the PtM channel 11 (step A13). Upon receiving theswitching instruction message, the user terminal 101 starts an operationof receiving the content on the PtM channel 11 and returns a switchingcompletion message to the base station control device 301 afterconfirming that the content can normally be received on the PtM channel11 (step A14).

Upon receiving the switching completion message, the base stationcontrol device 301 sends a PtP channel transmission stop message forcanceling the PtP channel 1 to the base station 201 (step A15). Uponreceiving the transmission stop message, the base station 201 stops thetransmission of the PtP channel 1. As a result, the radio channel usedfor the content distribution to the user terminal 101 is switched fromthe PtP channel 1 to PtM channel 11, and all the user terminals 101 to103 receive the content on the PtM channel 11, as shown in FIG. 12.

The base station 201 or base station control device 301 may send aninquiry message for inquiring of the user terminal 101 whether or notthe stop of the content reception on the PtP channel 1 and the start ofthe content reception on the PtM channel 11 are possible before thetransmission of the switching instruction message in step A13. In thiscase, the base station 201 or base station control device 301 sends theswitching instruction message at the time point when receiving an OKreply from the user terminal 101.

However, when receiving a reply indicating that it is impossible toperform a normal content reception from the user terminal 101 as aresult of the inquiry message, the base station 201 or base stationcontrol device 301 rearranges the transmission power of the PtM channel11 based on the current transmission power of the PtP channel 1, thecurrent reception power of the PtP channel 1 measured by the userterminal 101, and the like. After the rearrangement of the transmissionpower of the PtM channel 11, the base station 201 or base stationcontrol device 301 sends an inquiry message to the user terminal 101again.

In the channel switching process of step S7 (FIG. 3), a plurality of PtPchannels currently used for the content distribution to a plurality ofuser terminals may be switched to the PtM channel at a time. It goeswithout saying that the channel switching process of step S7 (FIG. 3)performed for a plurality of user terminals needs to be carried out suchthat the total of the downlink transmission power of the base station201 does not exceed the upper limit while the PtM channel is set withthe plurality of PtP channels maintained.

A case where the channel switching process of step S7 (FIG. 3) isperformed for the user terminals 102 and 103 under the condition shownin FIG. 6 will be described. FIG. 23 is a sequence chart showing anoperation in the case where the channel switching process of step S7(FIG. 3) is performed for the user terminals 102 and 103 under thecondition shown in FIG. 6. This process is performed after estimatingthe transmission power of the PtM channel that reaches the user terminal102 in step S5 of FIG. 2, comparing the estimated transmission power andthe margin power (Mgn_PW) in the cell 100 in step S6 of FIG. 3, andconfirming that the estimated transmission power is not more than themargin power (Mgn_PW).

When the channel switching process of step S7 (FIG. 3) is performed forthe user terminals 102 and 103 under the condition shown in FIG. 6, thebase station control device 301 sends a PtM channel transmission startmessage to the base station 201 to allow the base station 201 to startthe transmission of PtM channel 12 (see FIG. 13) that reaches the userterminal 102, as shown in FIG. 23 (step C1). Upon receiving the PtMchannel transmission start message, the base station 201 starts thetransmission of the PtM channel 12 while maintaining the PtP channels 2and 3 as shown in FIG. 13 and returns a transmission start completionmessage to the base station control device 301 (step C2).

Upon receiving the transmission start completion message, the basestation control device 301 sends switching instruction messages to theuser terminals 102 and 103 to instruct the user terminals 102 and 103 toreceive the content not on the PtP channels 2 and 3 but on the PtMchannel 12 (steps C3 and C4). Upon receiving the switching instructionmessages, the user terminals 102 and 103 start operations of receivingthe content on the PtM channel 12 and return switching completionmessages to the base station control device 301 after confirming thatthe content can normally be received on the PtM channel 12 (steps C5 andC7).

Upon receiving the switching completion messages from the user terminals102 and 103, the base station control device 301 sends PtP channeltransmission stop messages for canceling the PtP channels 2 and 3 to thebase station 201 (steps C6 and C8) Upon receiving the transmission stopmessages, the base station 201 stops the transmission of the PtPchannels 2 and 3. As a result, the radio channels used for the contentdistribution to the user terminals 102 and 103 are switched from the PtPchannels 2 and 3 to the PtM channel 12, and the user terminals 102 and103 receive the content on the PtM channel 12, as shown in FIG. 10.

As described above, it is possible to complete the switching process ofall the PtP channels being used for the broadcast-type service in thecell 100 to the PtM channel more quickly by switching a plurality of PtPchannels to the PtM channel at a time.

A case where the channel switching process of step S7 (FIG. 3) isperformed for the user terminals 101 to 103 that receive thebroadcast-type service in the cell 100 under the condition shown in FIG.6 will be described. This process is performed after comparing, in stepS6 (FIG. 3) the margin power (Mgn_PW) in the cell 100 and thetransmission power of the PtM channel 11 (see FIG. 14) that reaches theuser terminal 1, which is the transmission power (Max_PtM) estimated instep S2, and confirming that the transmission power (Max_PtM) is notmore than the margin power (Mgn_PW).

This process can be realized by slightly modifying the procedure shownin FIG. 23. When the channel switching process of step S7 (FIG. 3) isperformed for the user terminals 101 to 103 under the condition shown inFIG. 6, the base station control device 301 sends a transmission startmessage to the base station 201 to allow the base station 201 to startthe transmission of PtM channel 11 (see FIG. 14) that reaches the userterminal 101 in step C1. Therefore, the base station 201 starts thetransmission of PtM channel 11 while maintaining the PtP channels 1 to 3as shown in FIG. 14.

At the time when sending the switching instruction messages in steps C3and C4, the base station control device 301 also sends, to the userterminal 101, a switching instruction message for instructing the userterminal 101 to receive the content not on the PtP channel 1, but on thePtM channel 11. Accordingly, the user terminals 101 to 103 startoperations of receiving the content on the PtM channel 11, and the userterminal 101 returns a switching completion message to the base stationcontrol device 301 after confirming that the content can normally bereceived on the PtM channel 11, like the user terminals 102 and 103.

The base station control device 301 sends, to the base station 201,transmission stop messages for canceling the PtP channels 2 and 3 insteps C6 and C8 and, at the same time, sends, to the base station 201,another transmission stop message for canceling the PtP channel 1 inresponse to the switching completion message from the user terminal 110.The base station 201 accordingly stops the PtP channels 1 to 3. As aresult, the radio channels used for the content distribution to the userterminals 101 and 103 are switched from the PtP channels 1 to 3 to thePtM channel 11, and the user terminals 101 to 103 receive the content onthe PtM channel 11 as shown in FIG. 12.

When the base station 201 starts the transmission of the PtM channelwhile maintaining the PtP channel, the PtM channel is transmitted with atransmission power previously estimated as described above. In thiscase, a margin may be added to the estimated transmission power. Bythis, even when the user terminal that receives the PtM channel movesaway from the base station 201, it can receive the PtM channel. When theuser terminal that receives the content on the PtM channel detects anerror in the reception data, it may send an error detection notificationto the base station 201. In this case, the base station 201 increasesthe transmission power of the PtM channel in response to the errordetection notification.

In the channel switching process of step S7 (FIG. 3) performed for allthe user terminals 101 to 103, the base station 201 may start thetransmission of the PtM channel 10 having a transmission power higherthan one of the PtM channel 11 as shown in FIG. 16 instead of startingthe transmission of the PtM channel 11 as shown in FIG. 14, whilemaintaining the PtP channels 1 to 3. In this case, the radio channelsused for the content distribution to the user terminals 101 to 103 areswitched from the PtP channels 1 to 3 to the PtM channel 10, and theuser terminal 101 to 103 receive the content on the PtM channel 10 asshown in FIG. 15.

The base station 201 may increase the transmission power of the PtMchannel 11 after the radio channels of the user terminals 101 to 103have been switched to the PtM channel 11 as shown in FIG. 12 as a resultof the channel switching process of step S7 (FIG. 3) performed in thecondition shown in FIG. 10 or the channel switching process of step S7(FIG. 3) performed for all the user terminals 101 to 103, to therebygenerate the PtM channel 10 as shown in FIG. 15. It goes without sayingthat the total of the downlink transmission power of the base station201 should not exceed the upper limit even in the case where the PtMchannel 10 that reaches near the boundary of the cell 100 is generatedas described above.

Next, details of the channel switching process of step S9 (FIG. 3) willbe described with reference to the drawings.

FIG. 20 is a sequence chart showing an operation in the case where thechannel switching process of step S9 (FIG. 3) is performed under thecondition shown in FIG. 6. When the channel switching process of step S9(FIG. 3) is performed under the condition shown in FIG. 6, the basestation control device 301 sends, to the user terminal 103, a switchingpreparation instruction message for instructing the user terminal 103 tocancel the content reception operation on the PtP channel 3 and toperform preparation of receiving the content on the PtM channel 13 (seeFIG. 8) that reaches the user terminal 103, as shown in FIG. 20 (stepB1). The switching preparation instruction message includes informationrelated to time at which the PtM channel 13 can be received.

Upon receiving the switching preparation instruction. message, the userterminal 103 returns a switching preparation completion message to thebase station control device 301 (step B2).

In response to the switching preparation completion message, the basestation control device 301 sends, to the base station 201, atransmission stop message for canceling the PtP channel 3 (step B3).Upon receiving the transmission stop message, the base station 201 stopsthe transmission of the PtP channel 3. After that, the base station 201returns a transmission stop completion message to the base stationcontrol device 301 (step B4).

Upon receiving the transmission stop completion message, the basestation control device 301 sends, to the base station 201, atransmission start message for instructing the base station 201 to startthe transmission of the PtM channel 13 that reaches the user terminal103 (step B5). In response to the transmission start message, the basestation 201 starts the transmission of the PtM channel 13 as shown inFIG. 8 and returns a transmission start completion message to the basestation control device 301 (step B6).

The user terminal 103 starts an operation of receiving the content onthe PtM channel 13 at the time specified by the switching preparationinstruction message. As a result, the radio channel used for the contentdistribution to the user terminal 103 is switched from the PtP channel 3to the PtM channel 13, and the user terminal 103 receives the content onthe PtM channel 13 as shown in FIG. 8.

FIG. 21 is a sequence chart showing an operation in the case where thechannel switching process of step S9 (FIG. 3) is performed under thecondition shown in FIG. 8. When the channel switching process of step S9(FIG. 3) is performed under the condition shown in FIG. 8, the basestation control device 301 sends, to the user terminal 102, a switchingpreparation instruction message for instructing the user terminal 102 tocancel the content reception operation on the PtP channel 2 and toperform preparation of receiving the content on the PtM channel 12 (seeFIG. 10) that reaches the user terminal 102, as shown in FIG. 21 (stepB7). The switching preparation instruction message includes informationrelated to time at which the PtM channel 12 can be received. Uponreceiving the switching preparation instruction message, the userterminal 102 returns a switching preparation completion message to thebase station control device 301 (step B8).

In response to the switching preparation completion message, the basestation control device 301 sends, to the base station 201, atransmission stop message for canceling the PtP channel 2 (step B9).Upon receiving the transmission stop message, the base station 201 stopsthe transmission of the PtP channel 2. After that, the base station 201returns a transmission stop completion message to the base stationcontrol device 301 (step B10).

Upon receiving the transmission stop completion message, the basestation control device 301 sends, to the base station 201, atransmission power increase message for increasing the transmissionpower of the PtM channel 13 so that the PtM channel 13 can reach theuser terminal 102 (step B11). Upon receiving the transmission powerincrease message, the base station 201 increases the transmission powerof the PtM channel 13. As a result, the PtM channel 12 that reaches theuser terminal 102 is generated as shown in FIG. 10. After that, the basestation 201 returns a transmission power increase completion message tothe base station control device 301 (step B12).

The user terminal 102 starts an operation of receiving the content onthe PtM channel 12 at the time specified by the switching preparationinstruction message. As a result, the radio channel used for the contentdistribution to the user terminal 102 is switched from the PtP channel 2to the PtM channel 12, and the user terminals 102 and 103 receive thecontent on the PtM channel 12 as shown in FIG. 10.

FIG. 22 is a sequence chart showing an operation in the case where thechannel switching process of step S9 (FIG. 3) is performed under thecondition shown in FIG. 10. When the channel switching process of stepS9 (FIG. 3) is performed under the condition shown in FIG. 10, the basestation control device 301 sends, to the user terminal 101, a switchingpreparation instruction message for instructing the user terminal 101 tocancel the content reception operation on the PtP channel 1 and toperform preparation of receiving the content on the PtM channel 11 (seeFIG. 12) that reaches the user terminal 101, as shown in FIG. 22 (stepB13). The switching preparation instruction message includes informationrelated to time at which the PtM channel 11 can be received. Uponreceiving the switching preparation instruction message, the userterminal 101 returns a switching preparation completion message to thebase station control device 301 (step B14).

In response to the switching preparation completion message, the basestation control device 301 sends, to the base station 201, atransmission stop message for canceling the PtP channel 1 (step B15).Upon receiving the transmission stop message, the base station 201 stopsthe transmission of the PtP channel 1. After that, the base station 201returns a transmission stop completion message to the base stationcontrol device 301 (step B16).

Upon receiving the transmission stop completion message, the basestation control device 301 sends, to the base station 201, atransmission power increase message for increasing the transmissionpower of the PtM channel 12 so that the PtM channel 12 can reach theuser terminal 101 (step B17). Upon receiving the transmission powerincrease message, the base station 201 increases the transmission powerof the PtM channel 12. As a result, the PtM channel 11 that reaches theuser terminal 101 is generated as shown in FIG. 12. After that, the basestation 201 returns a transmission power increase completion message tothe base station control device 301 (step B18).

The user terminal 101 starts an operation of receiving the content onthe PtM channel 11 at the time specified by the switching preparationinstruction message. As a result, the radio channel used for the contentdistribution to the user terminal 101 is switched from the PtP channel 1to the PtM channel 11, and the user terminals 101 to 103 receive thecontent on the PtM channel 11 as shown in FIG. 12.

Next, details of the channel switching process of step S10 (FIG. 3) willbe described with reference to the drawings.

FIG. 24 is a sequence chart showing an operation in the case where thechannel switching process of step S10 (FIG. 3) (process in which PtPchannels 2 and 3 are switched to PtM channel at a time) is performedunder the condition shown in FIG. 6. When the channel switching processof step S10 (FIG. 3) is performed under the condition shown in FIG. 6,the base station control device 301 sends, to the user terminals 102 and103, switching preparation instruction messages for instructing the userterminals 102 and 103 to cancel the content reception operations on thePtP channels 2 and 3 and to perform preparations of receiving thecontent on the PtM channel 12 (see FIG. 10) that reaches the userterminal 102, as shown in FIG. 24 (steps D1 and D2). The switchingpreparation instruction messages include information related to time atwhich the PtM channel 12 can be received. Upon receiving the switchingpreparation instruction messages, the user terminals 102 and 103 returnswitching preparation completion messages to the base station controldevice 301 (steps D3 and D6).

In response to the switching preparation completion messages from theuser terminals 102 and 103, the base station control device 301 sends,to the base station 201, transmission stop messages for canceling thePtP channels 2 and 3 (steps D4 and D7). Upon receiving the transmissionstop messages, the base station 201 stops the transmission of the PtPchannels 2 and 3. After that, the base station 201 returns transmissionstop completion messages to the base station control device 301 (stepsD5 and D8).

Upon receiving the transmission stop completion messages, the basestation control device 301 sends, to the base station 201, atransmission start message for instructing the base station 201 to startthe transmission of the PtM channel 12 that reaches the user terminal102 (step D9). In response to the transmission start message, the basestation 201 starts the transmission of the PtM channel 12 as shown inFIG. 10 and returns a transmission start completion message to the basestation control device 301 (step D10).

The user terminals 102 and 103 start operations of receiving the contenton the PtM channel 12 at the time specified by the switching preparationinstruction messages. As a result, the radio channels used for thecontent distribution to the user terminals 102 and 103 are switched fromthe PtP channels 2 and 3 to the PtM channel 12, and the user terminals102 and 103 receive the content on the PtM channel 12 as shown in FIG.10.

While the PtM channel 12 is established after the cancels of the PtPchannels 2 and 3 in FIG. 24, it goes without saying that the PtM channel11 that reaches the user terminal 1 may be established after the cancelsof the PtP channels 1 to 3. In this case, the PtP channels 1 to 3 arecanceled in the condition shown in FIG. 6 and the PtM channel 11 thatreaches the user terminal 1 is established as shown in FIG. 12, with theresult that the user terminals 101 to 103 receive the content on the PtMchannel 11.

Next, an operation of the mobile communication system according to theembodiment of the present invention in the case where a plurality ofuser terminals to receive the broadcast-type service in the cell of thebase station 201 receive the content on the single PtM channel will bedescribed with reference to the drawings.

FIGS. 4 and 5 are flowcharts showing an operation of the mobilecommunication system according to the embodiment of the presentinvention in the case where the broadcast-type service is distributed onthe PtM channel.

The processing procedure shown in FIGS. 4 and 5 is activated when anyuser terminal that receives the broadcast-type service in the cell ofthe base station 201 cancels the reception of the broadcast-typeservice, or any user terminal that receives the broadcast-type servicein the cell of the base station 201 moves outside of the cell. That is,when the number of the user terminals that receive the broadcast-typeservice on the PtM channel in the cell is reduced, the procedure isactivated. For example, it is possible for the base station 201 and basestation control device 301 to recognize the number of the user terminalsthat are receiving the broadcast-type service by measuring the move-inof the user terminal to the cell and move-out thereof from the cell, orby sending a request signal to request the user terminal to report thelocation thereof as needed and receiving the report.

Alternatively, the processing procedure shown in FIGS. 4 and 5 may beperiodically activated with a predetermined interval. The reason for theabove is that even when the number of the user terminals that receivethe broadcast-type service on the PtM channel is not changed, thesituation in which the PtM channel needs to be switched to the PtPchannel depending on the location of the user terminal can occur. Forexample, in the case where the user terminal to receive thebroadcast-type service on the PtM channel moves to the location thatneeds less transmission power than the previous location does (ingeneral, in the case where the user terminal moves close to the basestation antenna), the above situation can occur.

Alternatively, the processing procedure shown in FIGS. 4 and 5 may beactivated when the allowable number of users that receive thebroadcast-type service is increased. When the allowable number of usersthat receive the broadcast-type service is increased, the transmissionpower that can be used for distribution of the broadcast-type service isincreased, with the result that the number of the user terminals thatcan receive the broadcast-type service on the PtP channel is increased.Accordingly, the processing procedure shown in the FIGS. 4 and 5 isactivated to determine whether a switching process from the PtM channelto the PtP channel is performed.

Alternatively, the processing procedure shown in FIGS. 4 and 5 may beactivated when the allowable number of users that receive thenon-broadcast-type service is reduced. When the allowable number ofusers that receive the non-broadcast-type service is reduced, thetransmission power that can be used for distribution of thebroadcast-type service is increased, with the result that the number ofthe user terminals that can receive the broadcast-type service on thePtP channel is increased. Accordingly, the processing procedure shown inthe FIGS. 4 and 5 is activated to determine whether a switching processfrom the PtM channel to the PtP channel is performed.

When one of the abovementioned conditions is satisfied to activate theprocessing procedure shown in FIGS. 4 and 5, the base station 201 or thebase station control device 301 estimates the transmission power of thePtP channel required in the case where the content is distributed on thePtP channel to all the plurality of user terminals that receive thebroadcast-type service on the PtM channel in the cell of the basestation 201 and calculates the total (TTL_PtP) of the transmission powerof all the PtP channels (step T1). The plurality of user terminalsmeasure the reception power of the radio channel transmitted from thebase station 201 to the user terminals and report the measurement resultto the base station 201 or base station control device 301, and therebythe base station 201 or base station control device 301 can estimate thetotal of the transmission power of the PtP channel. The radio channel isthe PtM channel that is being used for content distribution or a perchchannel that the plurality of user terminals are receiving or the like.The notification of the measurement result from the plurality of userterminals may be performed passively (in response to the measurementrequest instruction sent from the base station 201 or base stationcontrol device 301) or voluntarily or periodically.

The base station 201 or base station control device 301 estimates thetransmission power (Max_PtM) of the PtM channel that is being used forthe content distribution to the plurality of user terminals (step T2).The base station 201 or base station control device 301 then comparesthe total (TTL_PtP) calculated in step T1 and the transmission power(Max_PtM) calculated in step T2 (step T3). When the total (TTL_PtP) isnot less than the transmission power (Max_PtM) (No in step T3), the basestation 201 or base station control device 301 determines that aswitching process from the PtM channel to PtP channel need not beperformed to end this flow and waits for a new start condition.

On the other hand, when the total (TTL_PtP) is less than thetransmission power (Max_PtM) (Yes in step T3), the base station 201 orbase station control device 301 determines to perform the switchingprocess from PtM channel to PtP channel and estimates the power margin(Mgn_PW) in the cell of the base station 201 (step T4). The power margin(Mgn_PW) is a difference between the upper limit of the transmissionpower that the base station 201 can output to the cell and the total ofthe transmission power that the base station 201 outputs to all the userterminals (user terminals that receive the broadcast-type service in thecell and user terminals that receives the non-broadcast-type service inthe cell) in the cell.

The base station 201 or base station control device 301 specifies thePtP channel (hereinafter, referred to as “first PtP channel”) having themaximum power (Max_PtP) of the transmission powers of all the PtPchannels estimated in step T1 (step T5). The first PtP channel havingthe maximum power (Max_PtP) may be specified after the transmissionpower of the PtP channel has been estimated again in step T5.

The base station 201 or base station control device 301 compares thepower margin (Mgn_PW) and the estimated transmission power (Max_PtP) ofthe first PtP channel (step T6). When the power margin (Mgn_PW) is notless than the transmission power (Max_PtP) of the first PtP channel (Yesin step T6), a switching process from the PtM channel that is being usedfor the content distribution to the user terminal (hereinafter, referredto as “first user terminal”) to the first PtP channel in such a mannernot to interrupt the content reception operation in the first userterminal that is to receive the content on the first PtP channel of theplurality of user terminals (Step T7). In this channel switchingprocess, after the first PtP channel is established while the PtMchannel is maintained, the channel for distributing the content to thefirst user terminal is switched from the PtM channel to the establishedfirst PtP channel.

On the other hand, when the power margin (Mgn_PW) is less than theestimated transmission power (Max_PtP) of the first PtP channel (No instep T6), the base station 201 or base station control device 301estimates the transmission power (2nd_PtM) of the PtM channel thatreaches the user terminal (hereinafter referred to as “second userterminal”) that is to receive the PtP channel (hereinafter referred toas “second PtP channel”) having the second highest transmission power ofthe transmission powers of the PtP channels estimated in step T1 (stepT8). The transmission power (2nd_PtM) of the PtM channel that reachesthe second user terminal can be estimated based on the transmissionpower of the PtM channel that is being used for the content distributionto the plurality of user terminals and the reception power of the PtMchannel or perch channel in the second user terminal.

The base station 201 or base station control device 301 compares a valueobtained by adding the difference between the transmission power(Max_PtM) of the PtM channel that is being used for the contentdistribution to the plurality of user terminals and the transmissionpower (2nd_PtM) of the PtM channel that reaches the second user terminalto the power margin (Mgn_PW) with the transmission power (Max_PtP) ofthe first PtP channel (step T9).

When “Mgn_PW+(Max_PtM−2nd_PtM)≧Max_PtP” is satisfied (Yes in step T9), achannel switching process for the first user terminal is performed withinterruption of content reception operation (step T10). In this channelswitching process, the transmission power of the PtM channel that isbeing used for the content distribution to the plurality of userterminals is reduced such that the PtM channel cannot reach the firstuser terminal but can reach the second user terminal. After that, thefirst PtP channel is established, and the first user terminal receivesthe content on the established first PtP channel. Therefore, the contentreception operation in the first user terminal is interrupted during thetime period between the generation of PtM channel that reaches thesecond user terminal and the establishment of the first PtP channel.

When “Mgn_PW+(Max_PtM−2nd_PtM)<Max_PtP” is satisfied (No in step T9), achannel switching process for the plurality of user terminals thatreceive the broadcast-type service in the cell of the base station 201is performed with interruption of content reception operation (stepT11). In this channel switching process, after the transmission power ofthe PtM channel that is being used for the content distribution to theplurality of user terminals is reduced such that the PtM channel cannotreach the plurality of user terminals or PtM channel is canceled, thePtP channel is established between the plurality of user terminals andbase station 201, with the result that the plurality of user terminalsreceive the content on the established PtP channel. It goes withoutsaying that this channel switching process is performed such that thetotal of the downlink transmission power of the base station 201 doesnot exceed the upper limit of the transmission power that the basestation 201 can output to the cell 100. When the channel switchingprocess (step T11) is performed for all the user terminals that receivethe broadcast-type service in the cell, the total of the downlinktransmission power of the base station 201 does not exceed the upperlimit during the channel switching process (step T11). The reason isthat the total (TTL_PtP) calculated in step T1 is less than thetransmission power (Max_PtM) calculated in step T2 (see step T3).

After the process in steps T7, T10, or T11 has been completed, the flowadvances to step T12. The base station 201 or base station controldevice 301, which previously holds a target list in which all the userterminals that receive the broadcast-type service in the cell of thebase station 201 are registered, deletes the user terminals whosereception channel has been switched to the PtP channel in the any of theabove steps from the target list (step T12). The base station 201 orbase station control device 301 then determines whether the userterminal whose reception channel needs to be switched to PtP channelexists or not based on the target list (step T13).

If the user terminal that receives the broadcast-type service on the PtMchannel still exists (Yes in step T13), the base station 201 or basestation control device 301 shifts to step T4. On the other hand, if allthe user terminals that receive the broadcast-type service are receivingthe content on the PtP channel (No in step T13), the base station 201 orbase station control device 301 ends this flow and waits for a new startcondition.

Only a part of the user terminals that receive the broadcast-typeservice in the cell may be registered in the above target list, not allthe user terminals that receive the broadcast-type service in the cell.In this case, a mixed state of the PtP channel and PtM channel in thecell may arise temporary or constantly.

When the power margin (Mgn_PW) is less than the transmission power(Max_PtP) in step T6, it is determined, in step T9, which of the channelswitching processes of steps T10 and step T11 is performed. However, theprocesses of steps T8 to T10 may be omitted. In this case, when thepower margin (Mgn_PW) is less than the transmission power (Max_PtP) instep T6, the channel switching process (step T11) is performed.

When the total (TTL_PtP) is not less than the transmission power(Max_PtM) in step T3, it is determined that the channel switchingprocess from the PtM channel to PtP channel need not be performed.However, even when the total (TTL_PtP) is not less than the transmissionpower (Max_PtM), it may be determined to perform the channel switchingprocess depending on the security attribute of the content. For example,in the case where the content is paid content, the channel switchingprocess from the PtM channel to PtP channel may be performed.

Next, detail of the channel switching process of step T7 (FIG. 5) willbe described with reference to the drawings.

FIG. 25 is a sequence chart showing an operation in the case where thechannel switching process of step T7 (FIG. 5) is performed under thecondition shown in FIG. 12. When the channel switching process of stepT7 (FIG. 5) is performed under the condition shown in FIG. 12, the basestation control device 301 sends, to the base station 201, atransmission start message to allow the base station 201 to start thetransmission of PtP channel 1 (see FIG. 11), as shown in FIG. 25 (stepE1). Upon receiving the transmission start message, the base station 201starts the transmission of the PtP channel 1 while maintaining the PtMchannel 11 as shown in FIG. 11 and returns a transmission startcompletion message to the base station control device 301 (step E2).

Upon receiving the transmission start completion message, the basestation control device 301 sends, to the user terminal 101, a switchinginstruction message for instructing the user terminal 101 to receive thecontent not on the PtM channel 11 but on the PtP channel 1 (step E3).Upon receiving the switching instruction message, the user terminal 101starts an operation of receiving the content on the PtP channel 1 andreturns a switching completion message to the base station controldevice 301 after confirming that the content can normally be received onthe PtP channel 1 (step E4).

Upon receiving the switching completion message, the base stationcontrol device 301 sends, to the base station 201, a transmission powerreduction message for reducing the transmission power of the PtM channel11 such that the PtM channel 11 cannot reach the user terminal 101 butcan reach the user terminal 102 (step E5). Upon receiving thetransmission power reduction message, the base station 201 reduces thetransmission power of the PtM channel 11. As a result, the PtM channel12 that reaches the user terminal 102 is generated as shown in FIG. 10.After generating the PtM channel 12, the base station 201 returns atransmission power reduction completion message to the base stationcontrol device 301 (step E6). Thus, as shown in FIG. 10, the userterminal 101 receives the content on the PtP channel 1, and the userterminals 102 and 103 receive the content on the PtP channel 12.

Further, it is possible to perform the channel switching process of stepT7 (FIG. 5) under the condition shown in FIG. 15. When the switchingprocess of step T7 (FIG. 5) under the condition shown in FIG. 15 isperformed, the base station 201 starts the transmission of the PtPchannel 1 to the user terminal 101 while maintaining the PtM channel 10and reduces the transmission power of the PtM channel 10 as shown inFIG. 10 after the user terminal 101 starts the content receptionoperation on the PtP channel 1 to generate the PtM channel 12.

FIG. 26 is a sequence chart showing an operation in the case where thechannel switching process of step T7 (FIG. 5) is performed under thecondition shown in FIG. 10. When the channel switching process of stepT7 (FIG. 5) is performed under the condition shown in FIG. 10, the basestation control device 301 sends, to the base station 201, atransmission start message to allow the base station 201 to start thetransmission of PtP channel 2 (see FIG. 9), as shown in FIG. 26 (stepE7). Upon receiving the transmission start message, the base station 201starts the transmission of the PtP channel 2 while maintaining the PtMchannel 12 as shown in FIG. 9 and returns a transmission startcompletion message to the base station control device 301 (step E8).

Upon receiving the transmission start completion message, the basestation control device 301 sends, to the user terminal 102, a switchinginstruction message for instructing the user terminal 102 to receive thecontent not on the PtM channel 12 but on the PtP channel 2 (step E9).Upon receiving the switching instruction message, the user terminal 102starts an operation of receiving the content on the PtP channel 2 andreturns a switching completion message to the base station controldevice 301 after confirming that the content can normally be received onthe PtP channel 2 (step E10).

Upon receiving the switching completion message, the base stationcontrol device 301 sends, to the base station 201, a transmission powerreduction message for reducing the transmission power of the PtM channel12 such that the PtM channel 12 cannot reach the user terminal 102 butcan reach the user terminal 103 (step E11). Upon receiving thetransmission power reduction message, the base station 201 reduces thetransmission power of the PtM channel 12. As a result, the PtM channel13 that reaches the user terminal 103 is generated as shown in FIG. 8.After generating the PtM channel 13, the base station 201 returns atransmission power reduction completion message to the base stationcontrol device 301 (step E12). Thus, as shown in FIG. 8, the userterminals 101 and 102 receive the content on the PtP channels 1 and 2,and the user terminal 103 receives the content on the PtM channel 13.

FIG. 27 is a sequence chart showing an operation in the case where thechannel switching process of step T7 (FIG. 5) is performed under thecondition shown in FIG. 8. When the channel switching process of step T7(FIG. 5) is performed under the condition shown in FIG. 8, the basestation control device 301 sends, to the base station 201, atransmission start message to allow the base station 201 to start thetransmission of PtP channel 3 (see FIG. 7), as shown in FIG. 27 (stepE13). Upon receiving the transmission start message, the base station201 starts the transmission of the PtP channel 3 to the user terminal 3while maintaining the PtM channel 13 as shown in FIG. 7 and returns atransmission start completion message to the base station control device301 (step E14).

Upon receiving the transmission start completion message, the basestation control device 301 sends, to the user terminal 103, a switchinginstruction message for instructing the user terminal 103 to receive thecontent not on the PtM channel 13 but on the PtP channel 3 (step E15).Upon receiving the switching instruction message, the user terminal 103starts an operation of receiving the content on the PtP channel 3 andreturns a switching completion message to the base station controldevice 301 after confirming that the content can normally be received onthe PtP channel 3 (step E16).

Upon receiving the switching completion message, the base stationcontrol device 301 sends, to the base station 201, a transmission stopmessage for canceling the PtM channel 13 (step E17). Upon receiving thetransmission stop message, the base station 201 stops the transmissionof the PtM channel 13. Thus, as shown in FIG. 6, the user terminals 101to 103 receive the content on the PtP channels 1 to 3.

As described above, when the radio channel to be used for the contentdistribution to the user terminals 101 to 103 is switched from the PtMchannel 11 to the PtP channels 1 to 3, the actual transmission power ofthe PtP channels 1 to 3 may become more than the initially estimatedtransmission power (total (TTL_PtP) calculated in step T1 shown in FIG.4). In this case, the radio channels may be switched back to the PtMchannel 11.

In the channel switching process of step T7 (FIG. 5), the channelswitching process to the PtP channel is performed for only one of theplurality of user terminals that receive the content on the PtM channelas described above. Alternatively, however, the radio channel of aplurality of user terminals may be switched to the PtP channel at atime. It goes without saying that the channel switching process of stepT7 (FIG. 5) performed for a plurality of user terminals needs to becarried out such that the total of the downlink transmission power ofthe base station 201 does not exceed the upper limit while the PtPchannel is transmitted to a plurality of user terminals with theplurality of PtM channels maintained.

A case where the channel switching process of step T7 (FIG. 5) isperformed for the user terminals 101 and 102 under the condition shownin FIG. 12 will be described. This process is performed after comparingthe total of the estimated transmission power of the PtP channels 1 and2 with the margin power (Mgn_PW) in the cell 100 in step T6 of FIG. 5,and confirming that the total of the estimated transmission power of thePtP channels 1 and 2 is not more than the margin power (Mgn_PW).

When the channel switching process of step T7 (FIG. 5) is performed forthe user terminals 101 and 102 under the condition shown in FIG. 12, thebase station 201 starts the transmissions of the PtP channels 1 and 2 tothe user terminals 101 and 102, respectively, while maintaining the PtMchannel 11 and, after the user terminals 101 and 102 start receiving thecontent on the PtP channels 1 and 2, reduces the transmission power ofthe PtM channel 11 to generate the PtM channel 13 as shown in FIG. 8.Thus, as shown in FIG. 8, the user terminals 101 and 102 receive thecontent on the PtP channels 1 and 2, and the user terminal 103 receivesthe content on the PtM channel 13. It goes without saying that theabovementioned operation of the base station 201 is performed under thecontrol of the base station control device 301.

A case where the channel switching process of step T7 (FIG. 5) isperformed for the user terminals 101 to 103 under the condition shown inFIG. 12 will be described. This process is performed after comparing thetotal of the estimated transmission power of the PtP channels 1 to 3with the margin power (Mgn_PW) in the cell 100 in step T6 of FIG. 5, andconfirming that the total of the estimated transmission power of the PtPchannels 1 to 3 is not more than the margin power (Mgn_PW).

When the channel switching process of step T7 (FIG. 5) is performed forthe user terminals 101 to 103 under the condition shown in FIG. 12, thebase station 201 starts the transmissions of the PtP channels 1 to 3 tothe user terminals 101 to 103, respectively, while maintaining the PtMchannel 11 as shown in FIG. 14 and, after the user terminals 101 to 103start receiving the content on the PtP channels 1 to 3, stops thetransmission of the PtM channel 11 as shown in FIG. 6. Thus, as shown inFIG. 6, the user terminals 101 to 103 receive the content on the PtPchannels 1 to 3. It goes without saying that the abovementionedoperation of the base station 201 is performed under the control of thebase station control device 301.

Next, the details of the channel switching process of step T10 (FIG. 5)will be described with reference to the drawings.

FIG. 28 is a sequence chart showing an operation in the case where thechannel switching process of step T10 (FIG. 5) is performed under thecondition shown in FIG. 12. When the channel switching process of stepT10 (FIG. 5) is performed under the condition shown in FIG. 12, the basestation control device 301 sends, to the user terminal 101, a switchingpreparation instruction message for instructing the user terminal 101 tocancel the content reception operation on the PtM channel 11 and toperform preparation of receiving the content on the PtP channel 1 (seeFIG. 10), as shown in FIG. 28 (step F1). The switching preparationinstruction message includes information related to time at which thePtP channel 1 can be received. Upon receiving the switching preparationinstruction message, the user terminal 101 returns a switchingpreparation completion message to the base station control device 301(step F2).

Upon receiving the switching preparation completion message, the basestation control device 301 sends, to the base station 201, atransmission power reduction message for reducing the transmission powerof the PtM channel 11 such that the PtM channel 11 cannot reach the userterminal 101 but can reach the user terminal 102 (step F3). Uponreceiving the transmission power reduction message, the base station 201reduces the transmission power of the PtM channel 11. As a result, thePtM channel 12 that reaches the user terminal 102 is generated. Aftergenerating the PtM channel 12, the base station 201 returns atransmission power reduction completion message to the base stationcontrol device 301 (step F4).

Upon receiving the transmission power reduction completion message, thebase station control device 301 sends, to the base station 201, atransmission start message for allowing the base station 201 to startthe transmission of PtP channel 1 (step F5). In response to thetransmission start message, the base station 201 starts the transmissionof the PtP channel 1 to the user terminal 101 as shown in FIG. 10. Theuser terminal 101 starts receiving the content on the PtP channel 1 atthe time specified by the switching preparation instruction message. Asa result, the user terminal 101 receives the content on the PtP channel1, and the user terminals 102 and 103 receive the content on the PtMchannel 12 as shown in FIG. 10.

FIG. 29 is a sequence chart showing an operation in the case where thechannel switching process of step T10 (FIG. 5) is performed under thecondition shown in FIG. 10. When the channel switching process of stepT10 (FIG. 5) is performed under the condition shown in FIG. 10, the basestation control device 301 sends, to the user terminal 102, a switchingpreparation instruction message for instructing the user terminal 102 tocancel the content reception operation on the PtM channel 12 and toperform preparation of receiving the content on the PtP channel 2 (seeFIG. 8), as shown in FIG. 29 (step F6). The switching preparationinstruction message includes information related to time at which thePtP channel 2 can be received. Upon receiving the switching preparationinstruction message, the user terminal 102 returns a switchingpreparation completion message to the base station control device 301(step F7).

Upon receiving the switching preparation completion message, the basestation control device 301 sends, to the base station 201, atransmission power reduction message for reducing the transmission powerof the PtM channel 12 such that the PtM channel 12 cannot reach the userterminal 102 but can reach the user terminal 103 (step F8). Uponreceiving the transmission power reduction message, the base station 201reduces the transmission power of the PtM channel 12. As a result, thePtM channel 13 that reaches the user terminal 103 is generated. Aftergenerating the PtM channel 13, the base station 201 returns atransmission power reduction completion message to the base stationcontrol device 301 (step F9).

Upon receiving the transmission power reduction completion message, thebase station control device 301 sends, to the base station 201, atransmission start message for allowing the base station 201 to startthe transmission of PtP channel 2 (step F10). In response to thetransmission start message, the base station 201 starts the transmissionof the PtP channel 2 to the user terminal 102 as shown in FIG. 8. Theuser terminal 102 starts receiving the content on the PtP channel 2 atthe time specified by the switching preparation instruction message. Asa result, the user terminals 101 and 102 receive the content on the PtPchannels 1 and 2, and the user terminal 103 receives the content on thePtM channel 13 as shown in FIG. 8.

FIG. 30 is a sequence chart showing an operation in the case where thechannel switching process of step T10 (FIG. 5) is performed under thecondition shown in FIG. 8. When the channel switching process of step T1(FIG. 5) is performed under the condition shown in FIG. 8, the basestation control device 301 sends, to the user terminal 103, a switchingpreparation instruction message for instructing the user terminal 103 tocancel the content reception operation on the PtM channel 13 and toperform preparation of receiving the content on the PtP channel 3 (seeFIG. 6), as shown in FIG. 30 (step F11). The switching preparationinstruction message includes information related to time at which thePtP channel 3 can be received.

Upon receiving the switching preparation instruction message, the userterminal 103 returns a switching preparation completion message to thebase station control device 301 (step F12).

Upon receiving the switching preparation completion message, the basestation control device 301 sends, to the base station 201, atransmission stop message for canceling the PtM channel 13 (step F13).Upon receiving the transmission stop message, the base station 201 stopsthe transmission of the PtM channel 13 and returns a transmission stopcompletion message to the base station control device 301 (step F14).

Upon receiving the transmission stop completion message, the basestation control device 301 sends, to the base station 201, atransmission start message for allowing the base station 201 to startthe transmission of PtP channel 3 (step F15). In response to thetransmission start message, the base station 201 starts the transmissionof the PtP channel 3 to the user terminal 103 as shown in FIG. 6. Theuser terminal 103 starts receiving the content on the PtP channel 3 atthe time specified by the switching preparation instruction message. Asa result, the user terminals 101 to 103 receive the content on the PtPchannels 1 to 3 as shown in FIG. 6.

Next, the channel switching process of step T11 (FIG. 5) will bedescribed.

When the radio channel used for the content distribution to the userterminals 101 and 102 is switched from the PtM channel 11 to the PtPchannels 1 and 2 (see FIG. 8) at a time by the channel switching processof step T11 (FIG. 5) performed under the condition shown in FIG. 12, thebase station 201 reduces the transmission power of the PtM channel 11such that the PtM channel 11 cannot reach the user terminals 101 and 102but can reach the user terminal 103. As a result, the PtM channel 13that reaches the user terminal 103 is generated.

After that, the base station 201 starts the transmissions of the PtPchannels 1 and 2 to the user terminals 101 and 102 as shown in FIG. 8.The user terminals 101 and 102 accordingly receive the PtP channels 1and 2 as shown in FIG. 8. It goes without saying that the abovementionedoperation of the base station 201 is performed under the control of thebase station control device 301.

In the channel switching process of step T11 (FIG. 5) performed underthe condition shown in FIG. 12, the radio channel used for the contentdistribution to the user terminals 101 to 103 may be switched from thePtM channel 11 to the PtP channels 1 to 3 (see FIG. 6) at a time. Inthis case, the base station 201 stops the transmission of the PtMchannel 11, and starts the transmissions of the PtP channels 1 to 3 tothe user terminals 101 to 103 as shown in FIG. 6. As a result, the userterminals 101 to 103 receive the content on the PtP channels 1 to 3 asshown in FIG. 6. It goes without saying that the abovementionedoperation of the base station 201 is performed under the control of thebase station control device 301.

As described above, in the respective channel switching processes ofsteps S7, S9, S10, T7, T10, and T11 shown in FIGS. 3 and 5, the type ofthe radio channel is switched under the control of the base stationcontrol device 301. That is, the base station control device 301includes a channel switching control means for switching the radiochannel type, by which the respective channel switching processes ofsteps S7, S9, S10, T7, T10, and T11 shown in FIGS. 3 and 5 are realized.Further, it has been determined whether the radio channel type isswitched or not in the respective steps S3 and T3 shown in FIGS. 2 and4. The determination may be made by the base station 201 or base stationcontrol device 301, as described above. That is, the base station 201 orbase station control device 301 includes a channel switchingdetermination means for determining whether to switch the radio channeltype. The channel switching determination means determines whether toswitch the radio channel type from a first channel to second channeldifferent from the first channel based on the downlink transmissionpower of the first channel that is being used for the contentdistribution and the downlink transmission power of the second channelto be used for the content distribution.

The types of the content include the content whose distribution needs tobe performed without interruption and content whose distribution mightbe performed with interruption. A movie or broadcasting image can betaken as an example of the content whose distribution needs to beperformed without interruption. The content as described above isdistributed in successive manner, and an interruption of thedistribution causes discontent among users. Notification informationthat is distributed at a certain interval can be taken as the contentwhose distribution might be performed with interruption. The content asdescribed above is distributed intermittently or repeatedly and, if itsdistribution is interrupted, the users can obtain the missing dataagain.

The respective channel switching processes of steps S9, S10, T10, andT11 shown in FIGS. 3 and 5 involve the interruption of contentdistribution as described above. However, it is not desirable to performthe channel switching process involving the interruption of contentdistribution in the case where the content to be distributed to the userterminals that receive the broadcast-type service is the content whosedistribution needs to be performed without interruption. In this case,the channel switching process involving the interruption of contentdistribution may not be performed.

In order to allow the base station control device 301 to know whethercontent from the broadcast content server 501 is the content whosedistribution needs to be performed without interruption, the broadcastcontent server 501 notifies the base station control device 301 of theattribute of the content, that is, whether or not the content is thecontent whose distribution needs to be performed without interruption atthe time when the broadcast distribution of the content from thebroadcast content server 501 is started, or while the broadcastdistribution of the content is being performed. With the aboveconfiguration, the base station control device 301 can determine whetherto perform the channel switching process involving the interruption ofcontent distribution.

FIG. 31 shows an operation in which the broadcast content server 501notifies the base station control device 301 of the attribute of thecontent. FIG. 31A is a sequence chart showing an operation of notifyingof the content attribute at the time when the content distribution isstarted, and FIG. 31B is a sequence chart showing an operation ofnotifying of the content attribute or a change of the content attributewhile the content distribution is being performed.

In FIG. 31A, the broadcast content server 501 sends a content attributenotification message for notifying of the content attribute at the timewhen the content distribution is started (step G1). The base stationcontrol device 301 then sends a content attribute notificationconfirmation message to the broadcast content server 501 to notify thecontent server 501 that the base station control device 301 has receivedthe notification related to the content attribute (step G2). In FIG.31B, the broadcast content server 501 sends a content attribute changenotification message for notifying of the content attribute or a changeof the content attribute while the content distribution is beingperformed (step G3). The base station control device 301 then sends acontent attribute change notification confirmation message to thebroadcast content server 501 to notify the content server 501 that thebase station control device 301 has received the notification related tothe content attribute (step G4).

The present invention is not limited to the above representativeembodiment and those skilled in the art can make variations andmodifications without deviating from the broad principles and spirit ofthe present invention based on claims of the present invention. Theinvention obtained by the above variation and modification belongs tothe scope of the present invention. For example, although the channelswitching control means and channel switching control method in themobile communication system are realized by a program control in theabove embodiment, a software configuration and hardware configurationcan be employed as far as they can realize the functions described inclaims of the present invention. For example, a part or all of the aboveprogram control may be constituted by other logical circuits.

INDUSTRIAL APPLICABILITY

As described above, the present invention is suitably applied to themobile communication system in which the type of a radio channel usedfor the content distribution needs to be switched.

1. A content distribution system comprising: a base station whichutilizes at least one type of communication channel to distributecommunication data content between the base station and at least onemobile station; and the base station further comprising channeldetermination means which makes a determination of the at least one typeof communication channel to be used based on a transmission distributionpower of the communication data content to one of the at least onemobile station, wherein the at least one type of communication channel,further comprises: an individual communication channel and a commoncommunication channel the channel determination means bases thedetermination on a first downlink transmission power of the individualcommunication channel and a second downlink transmission power of thecommon communication channel, and the channel determination meansdetermines that the at least one type of communication channel isswitched from the individual communication channel to the commoncommunication channel when the second downlink transmission power isless than the first downlink transmission power.
 2. The contentdistribution system according to claim 1, wherein the channeldetermination means includes means for switching the at least one typeof communication channel from the individual communication channel tothe common communication channel as long as a total downlinktransmission power of the base station during the channel switching fromthe individual communication channel to the common communication channeldoes not exceed an upper limit of a transmission power that the basestation can output to a cell.
 3. The content distribution systemaccording to claim 2, wherein the individual communication channel isindividually assigned to the at least one mobile station, the commoncommunication channel is commonly assigned to the at least one mobilestation, and the channel determination means sequentially performs thechannel switching for the individual communication channel in anascending order of the transmission power required to complete thechannel switching from the individual communication channel to thecommon communication channel.
 4. The content distribution systemaccording to claim 2, wherein the common communication channel iscommonly assigned to the at least one mobile station, the individualcommunication channel is individually assigned to the at least onemobile station, and the channel determination means sequentially assignsthe individual communication channel to the at least one mobile stationin a descending order of the downlink transmission power of theindividual communication channel through which the at least one mobilestation receives the communication data content when the individualchannel is used for the distribution to complete the channel switchingfrom the common communication channel to the individual communicationchannel.
 5. The content distribution system according to claim 1,wherein the channel determination means bases the determination on atotal number of the at least one mobile station.
 6. The contentdistribution system according to claim 1, wherein the channeldetermination means bases the determination on an allowable number ofthe at least one mobile station that receive a service of thedistribution of the communication data content.
 7. The contentdistribution system according to claim 1, wherein the channeldetermination means bases the determination on an allowable number ofthe at least one mobile station that receive services other than that ofdistribution of the communication data content.
 8. The contentdistribution system according to claim 1, wherein the determination ofthe at least one type of communication channel between the base stationand the at least one mobile station is performed in the distribution ofthe communication data content.
 9. A channel determination method of acontent distribution system comprising: utilizing at least one type ofcommunication channel to distribute communication data content between abase station and at least one mobile station determining one of the atleast one type of communication channel used based on a transmissiondistribution power of the communication data content to one of the atleast one mobile station, wherein: the at least one type ofcommunication channel, further comprises: an individual communicationchannel and a common communication channel determining the one of the atleast one type of communication channel used on the basis of a firstdownlink transmission power of the individual communication channel anda second downlink transmission power of the common channel; determiningwhether the at least one type of communication channel is switched froman individual communication channel to a common communication channel onthe basis of a first downlink transmission power of the individualcommunication channel and a second downlink transmission power of thecommon communication channel when the common communication channel isbeing used; and determining the at least one type of communicationchannel is switched from the individual communication channel to thecommon communicatio channel when the second downlink transmission poweris less than the first downlink transmission power.
 10. The channelswitching control method according to claim 9 further comprising:determining the at least one type of communication channel is switchedfrom the individual communication channel to the common communicationchannel as long as a total downlink transmission power of the basestation during the channel switching does not exceed an upper limit of atransmission power that the base station can output to a cell.
 11. Thechannel switching control method according to claim 10 furthercomprising: assigning individually the individual communication channelto the at least one mobile station; assigning commonly the commoncommunication channel to the at least one mobile station; and performingsequentially the determining the at least one type of communicationchannel of the individual communication channel in an ascending order ofthe downlink transmission power to complete the channel switching fromthe individual communication channel to the common communicationchannel.
 12. The channel switching control method according to claim 10further comprising: assigning commonly the common communication channelto the at least one mobile station; individually assigning theindividual communication channel to the at least one mobile station; andwherein the determining the at least one type of communication channelfurther comprises: sequentially assigning the individual communicationchannel to the at least one mobile station in a descending order of thedownlink transmission power of the individual communication channelreceiving the communication data content through the at least one mobilestation when the individual communication channel is used for thedistribution; and completing the channel switching from the commoncommunication channel to the individual communication channel.
 13. Thechannel determination method according to claim 9 further comprising:determining the at least one type of communication channel on a basis ofa total number of the at least one mobile station.
 14. The channeldetermination method according to claim 9 further comprising:determining the at least one type of communication channel on the basisof an allowable number of the at least one mobile station that receive aservice of the distribution of the communication data content.
 15. Thechannel determination method according to claim 9 further comprising:determining the at least one type of communication channel on the basisof an allowable number of the at least one mobile station that receivemobile communication services other than the distribution of thecommunication data content.
 16. The channel switching control methodaccording to claim 9, wherein the determining of the at least one typeof communication channel between the base station and the at least onemobile station is performed in the distribution of the communicationdata content.
 17. A network comprising: at least one base station whichutilizes at least one type of communication channel to distributecommunication data content between the at least one base station and atleast one mobile station; channel switching determination means whichmakes a determination on the at least one type of communication channelto be used based on a transmission distribution power of thecommunication data content to one of the at least one mobile station,wherein the at least one type of communication channel, furthercomprises: an individual communication channel and a commoncommunication channel and base station control device which controls theat least one base station, wherein the channel determination means basesthe determination of whether the at least one type of communicationchannel is switched from an individual communication channel to a commoncommunication channel on a first downlink transmission power of theindividual communication channel and a second downlink transmissionpower of the common communication channel when a common communicationchannel transmission power is set between the first downlinktransmission power and the second downlink transmission power, and thechannel determination means bases the determination to switch from theindividual communication channel to the common communication channelwhen the second downlink transmission power is less than the firstdownlink transmission power.
 18. The network according to claim 17,wherein the base station control device based on the determinationdirects the at least one base station to switch the at least one type ofcommunication channel from the individual communication channel to thecommon communication channel as long as a total downlink transmissionpower of the at least one base station during the channel switching doesnot exceed an upper limit of a transmission power that the at least onebase station can output to a cell.
 19. The network according to claim18, wherein the individual communication channel is individuallyassigned to the at least one mobile station, the common communicationchannel is commonly assigned to the at least one mobile station, and thebase station control device sequentially performs the channeldetermination for the individual communication channel in an ascendingorder of the downlink transmission power to complete the channeldetermination from the individual communication channel to the commoncommunication channel.
 20. The network according to claim 18, whereinthe common communication channel is commonly assigned to the at leastone mobile station, the individual communication channel is individuallyassigned to the at least one mobile station, the base station controldevice sequentially assigns the individual communication channel to theat least one mobile station in a descending order of the downlinktransmission power of the individual communication channel, and the atleast one mobile station receives the communication data content todetermine the at least one type of communication channel when theindividual communication channel is used.
 21. The network according toclaim 17, wherein the channel determination means bases thedetermination on a total number of the at least one mobile station. 22.The network according to claim 17, wherein the channel determinationmeans bases the determination on an allowable number of the at least onemobile station that receives a distribution of the communication datacontent.
 23. The network according to claim 17, wherein the channeldetermination means bases the determination on an allowable number ofthe at least one mobile station that receives mobile communicationservices other than distribution of the communication data content. 24.The network according to claim 17, wherein the determination of the atleast one type of communication channel between the at least one basestation and the at least one mobile station is performed in thedistribution of the communication data content.
 25. A channeldetermination method of a network comprising: using at least one type ofcommunication channel to distribute communication data content betweenat least one base station and at least one mobile station; determiningthe at least one type of communication channel used based on atransmission distribution power of the communication data content to oneof the at least one mobile station, wherein the at least one type ofcommunication channel, further comprises: an individual communicationchannel and a common communication channel directing the at least onebase station by using a base station control device in the network;determining whether the at least one type of communication channel isswitch from an individual communication channel to a commoncommunication channel on the basis of a first downlink transmissionpower of the individual communication channel and a second downlinktransmission power of the common channel when a common communicationchannel transmission power is set between the first downlinktransmission power and the second downlink transmission power; anddetermining that the at least one type of communication channel isswitched from the individual communication channel to the commoncommunication channel when the second downlink transmission power isless than the first downlink transmission power.
 26. The channelswitching control method according to claim 25, further comprising:directing the base station by the base station device according to thedetermination to switch the at least one type of communication channelfrom the individual communication channel to the common communicationchannel as long as a total downlink transmission power of the at leastone base station during the channel switching does not exceed an upperlimit of a transmission power that the at least one base station canoutput to a cell.
 27. The channel switching control method according toclaim 26 further comprising: assigning individually the individualcommunication channel to the at least one mobile station; assigningcommonly the common communication channel to the at least one mobilestation; and sequentially performing the channel switching by the basestation device for the individual communication channel in an ascendingorder of a downlink transmission power to complete the channel switchingfrom the individual communication channel to the common communicationchannel.
 28. The channel switching control method according to claim 26further comprising: assigning commonly the common communication channelto the at least one mobile station; assigning individually theindividual communication channel to the at least one mobile station; andassigning sequentially the individual communication channel to the atleast one mobile device by the base station device in a descending orderof downlink transmission power of the individual communication channelthrough which the at least one mobile station receives the communicationdata content when used.
 29. The channel switching control methodaccording to claim 25 further comprising: determining the at least onetype of communication channel on the basis of a total number of the atleast one mobile station.
 30. The channel switching control methodaccording to claim 25 further comprising: determining the at least onetype of communication channel on the basis of an allowable number of theat least one mobile station that receives a distribution of thecommunication data content.
 31. The channel switching control methodaccording to claim 25 further comprising: determining the at least onetype of the communication channel on the basis of an allowable number ofthe at least one mobile stations that receive mobile communicationservices other than a distribution of the communication data content.32. The channel switching control method according to claim 25, whereinthe determining of the at least one type of communication channelbetween the at least one base station and the at least one mobilestation is performed in the distribution of the communication datacontent.
 33. A content distribution system comprising: a base stationwhich utilizes at least one of an individual communication channel and acommon communication channel to distribute communication data contentbetween the base station and at least one mobile station, wherein thebase station further comprising channel adjustment means which adjusts atransmission power of the individual communication channel and atransmission power of the common communication channel so that a totaltransmission power of the individual communication channel and thecommon communication channel comply with a predetermined value; andchannel determination means which bases a determination on a firstdownlink transmission power of the individual communication channel anda second downlink transmission power of the common communication channelwherein; the channel determination means determines that at least onetype of communication channel is switched from the individualcommunication channel to the common communication channel when thesecond downlink transmission power is less than the first downlinktransmission power.